无法使用 Child class' object 访问 parent class' 全局变量

Question

我想在有人租车时更新可用汽车的计数器。当我尝试通过 child class 访问此变量时，它显示错误为“UnboundLocalError：赋值前引用的局部变量 'available_cars'”

PS: 还在努力中，所以我还没有完成所有的方法代码。

Parent Class

available_cars = 1000

class Car_rental():

def __init__(self):
    pass

def display_available_cars(self):
    print("Total avaialable cars for renting is:", available_cars)

def rent_hourly(self, cars_rented):
    print("Our hourly rate is 0/hr.")

    if cars_rented > available_cars:
        print("Sorry! We currently do not have the number of cars requested. You can have {} cars for now if you want.".format(
            available_cars))
    elif cars_rented < available_cars:
        print("Thank you for renting {} cars from Swift car renting portal. Enjoy you ride.".format(
            cars_rented))

    elif cars_rented < 0:
        print ("Please provide a valid number of cars.")

def rent_weekly(self):
    pass

def rent_monthly(self):
    pass

def bill(self):
    pass

def update_invetory(self, cars_rented):
    available_cars = available_cars - cars_rented

Child Class

从汽车租赁进口 *

class 客户(Car_rental): def init(self): Car_rental.init(self)

def rent_cars(self):

    mode = int(input(
        "Please select the mode of renting the car:\n1. Hourly\n2. Weekly\n3. Monthly\n"))
    if mode == 1 or mode == 'hourly' or mode == 'Hourly':
        cars_rented = int(input("How many cars do you wish to rent?"))
        self.rent_hourly(cars_rented)
        self.update_invetory(cars_rented)

    elif mode == 2 or mode == 'weekly' or mode == 'Weekly':
        self.rent_weekly()
    elif mode == 3 or mode == 'monthly' or mode == 'Monthly':
        self.rent_monthly()
    else:
        print("Please provide appropriate input.")

def return_cars(self):
    pass

Answer 1

因此，如果我正确地理解了你的问题，那么你的代码似乎有目标。

你想定义一个Car_Rentalclass，带有class级变量available_cars，初始设置为1000，然后作为客户租用车辆减少可用汽车的数量。
您还需要第二个客户 class 继承 Car_Rental class 实现计费功能。
虽然我不确定这一点，但您似乎还希望这些 class 定义中的每一个都驻留在它们自己单独的 python 脚本文件中。

这就是我解决这些问题的方式。

# If desired could be placed in separate file Car_Rental.py
class Car_Rental():
    available_cars = 1000

    def display_available_cars(self):
        print("Total avaialable cars for renting is:", Car_Rental.available_cars)

    def isOkayToRent(self, nmbr):
        return nmbr <= Car_Rental.available_cars
    
    def rent_hourly(self, cars_rented):
        print("Our hourly rate is 0/hr.")

        if cars_rented < 0:
            print ("Please provide a valid number of cars.")
            
        else:
            if self.isOkayToRent(cars_rented):
                print("Thank you for renting {} cars from Swift car renting portal. Enjoy you ride.".format(
                cars_rented))
            else:
                print("Sorry! We currently do not have the number of cars requested. You can have {} cars for now if you want.".format(
                Car_Rental.available_cars))
                
    def rent_weekly(self):
        pass

    def rent_monthly(self):
        pass

    def bill(self):
        pass

    def update_inventory(self, nmbr):                       
        assert nmbr > 0
        Car_Rental.available_cars -= nmbr
        
    @property
    def cars(self):
        return Car_Rental.available_cars

# Can be placed in  second file. 

#Note include this next line if classes are stored in separate files 
#from Car_rental import Car_Rental 


class Customer(Car_Rental): 
    def __init__(self):
        Car_Rental.__init__(self)

    def rent_cars(self):

        mode = int(input(
            "Please select the mode of renting the car:\n1. Hourly\n2. Weekly\n3. Monthly\n"))
        if mode == 1:
            cars_rented = int(input("How many cars do you wish to rent?"))
            self.rent_hourly(cars_rented)
            self.update_inventory(cars_rented)

        elif mode == 2:
            self.rent_weekly()
        elif mode == 3:
            self.rent_monthly()
        else:
            print("Please provide appropriate input.")

    def return_cars(self):
        pass

使用：

c1 = Customer()
c1.cars

1000

c1.rent_cars()  
Please select the mode of renting the car:
1. Hourly
2. Weekly
3. Monthly
How many cars do you wish to rent? 2
Our hourly rate is 0/hr.
Thank you for renting 2 cars from Swift car renting portal. Enjoy you ride.

为了说明适当的库存减少： c1.cars 产量 998

无法使用 Child class' object 访问 parent class' 全局变量

Unable to access parent class' global variable with Child class' object

global-variables

object

python-3.x